Methods have been developed which allow us to measure the in vitro rate of incorporation of leucine into renin. Experiments will be done to determine which factors control the rate of synthesis. Incubation of slices in differing concentrations of electrolytes and drugs (epinephrine, angiotensin) will be done in order to determine if these substances known to affect secretion rates will also alter synthesis. In addition, methods have been worked out using electron probe analysis which allows us to measure electrolyte concentrations in thin tissue slices, using a beam diameter of only 1 micron. We plan to measure intracellular concentrations of Na in tubular cells during different states of salt and water balance.